HKB
recognise its merit, and to work it into shape; but if worthless, he spoke out his mind at once, dissuading the projector from wasting upon it further labour or expense.
One of the important branches of practical mechanics to which Clement continued through life to devote himself, was the improvement of self-acting tools, more especially of the slide-lathe. He introduced various improvements in its construction and arrangement, until in his hands it became as nearly perfect as it was possible to be. In 1818, he furnished the lathe with a slide rest twenty-two inches long, for the purpose of cutting screws, provided with the means of self-correction; and some years later, in 1827, the Society of Arts awarded him their gold Isis medal for his improved turning-lathe, which embodied many ingenious contrivances calculated to increase its precision and accuracy in large surface-turning.
The beautiful arrangements embodied in Mr. Clement's improved lathe can with difficulty be described in words; but its ingenuity may be inferred from a brief statement of the defects which it was invented to remedy, and which it successfully overcame. When the mandrill of a lathe, having a metal plate fixed to it, turns round with a uniform motion, and the slide rest which carries the cutter is moving from the circumference of the work to the centre, it will be obvious that the quantity of metal passing over the edge of the cutter at each revolution, and therefore at equal intervals of time, is continually diminishing, in exact proportion to the spiral line described by the cutter on the face of the work. But in turning metal plates it is found very in expedient to increase the speed of the work beyond a certain quantity; for when this happens, and the tool passes the work at too great a velocity, it heats, softens, and is ground away, the edge of the cutter becomes dull, and the surface of the plate is indented and burnished, instead of being turned. Hence loss of time on the part of the workman, and diminished work on the part of the tool, results which, considering the wages of the one and the capital expended on the construction of the other, are of no small importance; for the prime objects of all improvement of tools are, economy of time and economy of capital--to minimize labour and cost, and maximize result.
The defect to which we have referred was almost the only remaining imperfection in the lathe, and Mr. Clement overcame it by making the machine self-regulating; so that, whatever might be the situation of the cutter, equal quantities of metal should pass over it in equal times,--the speed at the centre not exceeding that suited to the work at the circumference,--while the workman was enabled to convert the varying rate of the mandrill into a uniform one whenever he chose. Thus the expedients of wheels, riggers, and drums, of different diameters, by which it had been endeavoured to alter the speed of the lathe-mandrill, according to the hardness of the metal and the diameter of the thing to be turned, were effectually disposed of. These, though answering very well where cylinders of equal diameter had to be bored, and a uniform motion was all that was required, were found very inefficient where a Plane surface had to be turned; and it was in such cases that Mr. Clement's lathe was found so valuable. By its means surfaces of unrivalled correctness were produced, and the slide-lathe, so improved, became recognised and adopted as the most accurate and extensively applicable of all machine-tools.